See also

Poisoning – Acute guidelines for initial management
Resuscitation

Key points

1. Clinical features of phenobarbitone poisoning are due to depression of the central nervous system and effect on the cardiovascular system.
2. Onset of clinical features is usually within an hour of ingestion.
3. Management of phenobarbitone poisoning is supportive.

For 24 hour advice, contact Victorian Poisons Information Centre 13 11 26

Background

Clinical features due to phenobarbitone ingestion are mainly due to central nervous system depression and effect on the cardiovascular system. Symptoms include lethargy, slurred speech, ataxia, hypotension and arrhythmias.
Onset of symptoms is usually within an hour of ingestion and symptoms may be profound and prolonged.

Serum phenobarbitone concentrations can be useful for confirming the ingestion but are not a reliable predictor of clinical course.  

Patients requiring assessment

All children with deliberate self-poisoning or significant (>5 mg/kg OR >10 mg/kg greater than the child’s normal therapeutic dose if on regular dose) accidental ingestion
Any symptomatic child
Acute ingestion of unknown quantity
Any child where the developmental age is inconsistent with accidental poisoning as non-accidental poisoning should be considered.

Risk Assessment

History

Intentional overdose or accidental
Dose:

• Stated or likely dose taken
• Presented as syrup or immediate-release tablets
• If possible determine the exact name and tablet size.
• Calculate the maximum possible dose per kg

Co-ingestants eg paracetamol

Examination

• CNS
• Lethargy, slurred speech, ataxia, respiratory depression, coma. Large ingestions can mimic brain death.
• CVS
• Hypotension, Arrhythmias

Always check for Medicalert bracelet in any unconscious patient, or any other signs of underlying medical condition (fingerprick marks etc)

Consider the possibility of co ingestions, either accidental or deliberate

Investigations

ECG: (initially and repeat at 6 hours until normal).  

Paracetamol concentration in all intentional overdoses

If phenobarbitone serum concentrations performed:

• >172-258 micromol/L – may be expected to cause toxic effects
• >345-650 micromol/L – potential to be lethal

Acute Management

Patients Requiring Treatment

• All symptomatic children
• Acute ingestion of unknown quantity
• Based on ingestion amount:
• Phenobarbitone ingestion of >5mg/kg OR >10mg/kg greater than the child’s normal therapeutic dose if child is on maintenance phenobarbitone treatment

Resuscitation

• Standard procedures and supportive care. See also Resuscitation guideline and Poisoning – Guidelines for initial management.

Decontamination 

• Multidose activated charcoal via NGT after intubation increases phenobarbitone elimination and may reduce length of coma in children with large ingestions, provided bowel sounds are present. Discuss with a toxicologist via the Poisons Information Centre 13 11 26.

Mild symptoms

(eg ataxia, blurred vision)

• Observe 6 hours
• Discharge once symptom-free

Moderate-to-severe or persistent symptoms after 6 hours of observation

(eg Depressed conscious state or cardiac arrhythmias)

• Admit for observation and supportive management
• Phenobarbitone serum concentration at 6 hours if ongoing symptoms
  • If drug concentration increasing or above therapeutic range, admit for ongoing observation and serial drug concentration monitoring in consultation with toxicologist
• Discussion with toxicologist
• Discussion with paediatric intensive care team if severe symptoms

When to admit/consult local paediatric team, or who/when to phone

Admission should be considered for all children with an intentional overdose or in children with persisting symptoms after 6 hours observation.

Consult Contact Victorian Poisons Information Centre 13 11 26 for advice

When to consider transfer to a tertiary centre

Children with severe symptoms and/or the potential to require intensive care review.

For emergency advice and paediatric or neonatal ICU transfers, call the Paediatric Infant Perinatal Emergency Retrieval (PIPER) Service: 1300 137 650.

Discharge Criteria

Normal GCS
Normal ECG
Period of observation as above
For deliberate ingestion a risk assessment should indicate that the child is at low risk of further self-harm in the discharge setting

Discharge information and follow-up

Poisoning prevention for children Parent information

Victorian Poisons Information Centre: 13 11 26 www.austin.org.au/poisons

Intentional self-harm: Referral to local mental health services e.g. Orygen Youth Health: 1800 888 320 

Recreational poisoning: Referral to YoDAA, Victoria's Youth Drug and Alcohol Advice service: 1800 458 685

Last Updated December 2017